Internal combustion engine design has been subject to constant modifications and redesigns since its inception with the specific purpose of improving engine operating efficiency. Many improvements, however, that are directed toward improving engine efficiency are often not practical or are so costly that no real savings can be appreciated.
One particular line of internal combustion engine modifications for increasing engine output efficiency involves the alteration of the traditional four-stroke cycle. A typical four-stroke engine cycle is defined as including an intake stroke, a compression stroke, a power stroke, and an exhaust stroke. For its operation, at least one reciprocating piston is moved within a cylinder bore from a top dead center position (hereinafter abbreviated TDC) to a bottom dead center position (hereinafter abbreviated BDC), with four strokes occurring over two revolutions of the engine output shaft. Typically, in a first revolution, the piston will move inwardly from the TDC to BDC positions, defining the intake stroke during which an intake valve is opened so that an air/fuel mixture is suctioned into the engine cylinder above the piston. Thereafter, a compression stroke takes place as the piston moves outwardly so as to reduce the volume of the air/fuel mixture and increase the pressure within the engine cylinder prior to combustion of the explosive mixture. Normally, just before the beginning of the second revolution, the air fuel mixture is ignited at a point near the TDC position after which the power expansion stroke results causing the inward travel of the piston. Thereafter, the exhaust stroke occurs while the piston moves outwardly, as a result of which the exhaust gases are pumped through an exhaust valve that is opened in synchronization to the engine output shaft.
A conventional internal combustion engine includes a connecting rod pivotally connected via a wrist pin at one end to the piston and at another end to an offset portion of the output shaft for translating the reciprocal piston motion to the output shaft. The offset portion is spaced from the axis of rotation of the output shaft. The degree of offset defines the amount of leverage or the magnitude of the force moment acting on the output shaft since the leverage or moment is a function of the applied force as well as the distance between the applied force and the axis of rotation. During the power expansion stroke of the four-stroke cycle, chemical energy from the combustion of the air/fuel mixture is converted to linear motion of the piston caused by the expansion of the combusted gases. This energy is utilized to turn the engine output shaft and is released within each cylinder once during each two revolutions of the engine output shaft. Thus, it can be seen that the provision of multiple engine cylinders increases the number of times that an engine output shaft is powerfully driven during each revolution.
This conversion of chemical energy to transitional work of the piston is of course another area in which gains in efficiency have been advanced. Moreover, in modern engines, advances have also been made regarding the preparation of the air/fuel mixture by way of improved carburetors, fuel injection systems, and super-chargers.
However, even in light of the recent developments regarding fuel conversion to energy and fuel consumption efficiency, modern engines still run inefficiently with regard to the ability of the engine to actually convert the energy released by combustion into actual work output from the engine. To improve this, it is necessary to improve the manner in which the potential work available from the reciprocating piston is translated to the engine output shaft or output shaft.
When considering the forces that coact within the engine cylinder between the piston and the output shaft during the power expansion stroke, it will be appreciated that the pressure/force magnitude constantly decreases. The leverage arm, defined as the distance between the point of connection of the connecting rod to the output shaft and the axis of rotation of the output shaft, increases as the piston moves from the TDC position to a position approximately 90 degrees after TDC, after which it decreases. Neither the force applied to the piston from combustion nor the leverage arm decrease or increase linearly.
Since work is dependent on the product of distance times the force applied thereto, the reciprocating movement of the piston as driven during the power stroke becomes the potential work that is available to drive the output shaft. Thus, the ability and goal of an engine to most efficiently make use of the chemical energy provided from combustion is to find a way to more efficiently transfer the potential work from the reciprocating piston to the rotating output shaft.
There are many known methods and work paths to permit the piston to travel from TDC to BDC and transfer a portion of its available potential work to a rotary member or shaft. These include a conventional output shaft, a camdisk, a camdrum, and a gear chain. The common failure in each of these approaches is their inability to provide a consistent force magnitude to the rotating output shaft throughout the entire rotational arc through which an individual piston stroke acts. Rather, what these known engines have done is to deliver an erratic and inconsistent force to the rotating output shaft while applying some random magnitude of force during the rotational arc throughout which each individual piston acts. An example is shown in U.S. Pat. No. 2,006,498 to Dassett, that utilizes a noncircular cam-type output shaft for transferring the work from the piston. Although this patent does inherently provide a cam profile that modifies the leverage arm acting on the output shaft, it does not attempt to provide a consistent force magnitude to the engine output shaft throughout the entire rotational arc through which an individual piston stroke acts. More specifically, the device includes a cam profile which, at the start of the downward stroke of the piston during expansion, produces a rapid displacement of the piston to thereby permit a quick expansion stroke for greater mechanical efficiency and less heat production. However, because the patent does not realize that it is important to provide a consistent torque throughout the power stroke, the Dassett device falls far short of the extent to which the leverage arm can be modified.
Other types of prior art devices that modify the piston strokes of a four cycle internal combustion engine are disclosed in U.S. Pat. No. 4,467,756 to McWhorter and U.S. Pat. No. 4,466,403 to Menton. These devices include a means to modify the crank offset or leverage arm during the course of engine operation. Specifically, the crank arm is effectively lengthened before the power expansion stroke for providing an increased leverage to produce greater torque by increasing the mechanical advantage during the power stroke. Although these devices increase engine output torque and may improve engine efficiency to at least some degree, they do not modify the crank offset during the power stroke nor do they attempt to provide a consistent force magnitude.
Many other types of cam-driven output shaft internal combustion engines are known in the prior art including those with specifically designed cam paths that are altered to provide variable stroke mechanisms. That is to say, certain of the strokes of the typical four-cycle are modified to change the length of stroke and/or timing. An example is shown in U.S. Pat. No. 1,728,363 to Rightenour, which discloses a double cam device for providing two reciprocating piston motions during a single output shaft rotation, wherein the cam profiles are modified specifically for varying piston speed during certain stroke instances and defining different stroke lengths depending on the stroke. Moreover, Rightenour recognizes that using a rapid movement cam profile during the firing stroke provides a modified leverage at a specific point. Again, however, the cam path is not tailored for maximizing engine operating efficiency in the translation of reciprocal motion to rotary motion.
The devices disclosed in the following U.S. Pat. No. 3,895,614 to Bailey, U.S. Pat. No. 3,687,117 to Panariti, U.S. Pat. No. 1,209,708 to Houlehan, U.S. Pat. No. 879,289 to Mayo et al., U.S. Pat. No. 1,748,443 to Dawson, and U.S. Pat. No. 2,528,386 to Napper are of interest for their disclosure of engine output cam shafts which include guide tracks defined on a disc-like member associated with the output shaft and where the piston includes a roller or pin-type mechanism that is guided within the guide tracks. The guide tracks are used to translate the reciprocating motion of the piston into rotary motion of the output shaft. These patents disclose various guide paths for translating the reciprocating to rotary motion; however, they do not attempt to increase the output efficiency by providing a consistent torque magnitude to the output shaft.
U.S. Pat. No. 5,060,603 to Williams discloses a device for increasing an internal combustion engine's output efficiency by improving the efficiency of energy conversion from a reciprocating piston motion to rotary output shaft motion. Specifically, it accomplishes this by providing at last one disc-like element rotatably fixed to the engine output shaft, the disc-like element having a work receiving guide groove defined therein which engages with a lower end of a connecting rod pivotally extending from the reciprocating piston. The work receiving guide groove increases the length of the leverage arm while the pressure force acting on the reciprocating piston decreases to provide a substantially constant torque during the expansion stroke. However, the work receiving guide groove is designed by taking into account only a single cylinder and ignoring the contributions and parasitic effects of the other cylinders. As a result, because it does not account for the erratic demands of the parasitic cylinders, the work receiving guide groove provides an erratic torque output rather than the desired uniform torque output.
It is clear from the above that many attempts have been made to improve engine operating efficiency with respect to the manner of translation of reciprocating motion of a piston to the rotary motion of a crank or cam-type output shaft including the use of additional leverage providing mechanisms or cam profiles affecting piston speed. However, none of these prior art references have contemplated that it is necessary to provide a consistent total force magnitude from all cylinders, including the parasitic effects of cylinders which are not in their power stroke, to the engine output shaft.